The field of the invention relates generally to rotating machinery, and more specifically, to a system and method for creep measurement of rotating components.
As rotatable machines operate, a condition of components of the machine may deteriorate over time. This degradation of condition typically affects performance. Degradation may be due to various factors. One such factor is the deformation of the material of the component when exposed to stresses less than its yield strength over time, via a mechanism commonly referred to as creep. Creep can degrade gaps between parts that move relative to each other and can create projectile hazards and debris if the creep is permitted to occur until failure of the component material. Some components, such as turbine blades, are difficult or costly to remove from service for periodic inspections, and scheduled shutdowns for plant maintenance and repair may occur infrequently enough that creep may cause damage before it can be detected and repaired.
A method has been demonstrated to measure strain of rotating components such as turbine parts, using a periodic pattern printed on a part, compared against a referenced pattern to create a moiré pattern. In this method, the moiré pattern created is entirely assumed to be the result of the surface strain or creep of the part, without accounting for any miss-alignment, equipment change, or environmental changes. Hence, there is a need to separately recognize and correct the contribution of these factors in the creation of the moiré pattern, and thereby more accurately measure the actual creep that is undergone by the parts.